Re: [RESEND v3 1/1] i2c: qcom-geni: Disable DMA processing on the Lenovo Yoga C630

From: Stephen Boyd <swboyd@chromium.org>
To: Lee Jones <lee.jones@linaro.org>,
	agross@kernel.org, alokc@codeaurora.org,
	bjorn.andersson@linaro.org, mark.rutland@arm.com,
	robh+dt@kernel.org, vkoul@kernel.org, wsa@the-dreams.de
Cc: linux-i2c@vger.kernel.org, linux-arm-msm@vger.kernel.org,
	devicetree@vger.kernel.org, Lee Jones <lee.jones@linaro.org>
Subject: Re: [RESEND v3 1/1] i2c: qcom-geni: Disable DMA processing on the Lenovo Yoga C630
Date: Thu, 05 Sep 2019 22:33:08 -0700	[thread overview]
Message-ID: <5d71ef95.1c69fb81.6d090.085d@mx.google.com> (raw)
In-Reply-To: <20190905192412.23116-1-lee.jones@linaro.org>

Quoting Lee Jones (2019-09-05 12:24:12)
> We have a production-level laptop (Lenovo Yoga C630) which is exhibiting
> a rather horrific bug.  When I2C HID devices are being scanned for at
> boot-time the QCom Geni based I2C (Serial Engine) attempts to use DMA.
> When it does, the laptop reboots and the user never sees the OS.
> 
> Attempts are being made to debug the reason for the spontaneous reboot.
> No luck so far, hence the requirement for this hot-fix.  This workaround
> will be removed once we have a viable fix.
> 
> Signed-off-by: Lee Jones <lee.jones@linaro.org>
> ---
>  drivers/i2c/busses/i2c-qcom-geni.c | 12 ++++++++----
>  1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-qcom-geni.c b/drivers/i2c/busses/i2c-qcom-geni.c
> index a89bfce5388e..17abf60c94ae 100644
> --- a/drivers/i2c/busses/i2c-qcom-geni.c
> +++ b/drivers/i2c/busses/i2c-qcom-geni.c
> @@ -355,11 +355,13 @@ static int geni_i2c_rx_one_msg(struct geni_i2c_dev *gi2c, struct i2c_msg *msg,
>  {
>         dma_addr_t rx_dma;
>         unsigned long time_left;
> -       void *dma_buf;
> +       void *dma_buf = NULL;
>         struct geni_se *se = &gi2c->se;
>         size_t len = msg->len;
>  
> -       dma_buf = i2c_get_dma_safe_msg_buf(msg, 32);
> +       if (!of_machine_is_compatible("lenovo,yoga-c630"))

This compatible isn't in the 5.3 rc series nor is it in linux-next yet.
Is this "hot-fix" for the next merge window? Or is this compatible
string being generated by firmware somewhere and thus isn't part of the
kernel?

> +               dma_buf = i2c_get_dma_safe_msg_buf(msg, 32);
> +
>         if (dma_buf)
>                 geni_se_select_mode(se, GENI_SE_DMA);
>         else